United States healthcare costs are rising inexorably. Patients who have multiple co-morbidities account for a substantial portion of healthcare costs, and efforts to 'bend the cost curve' tend to focus on this patient population. Low back pain is an increasingly common diagnosis among older adults, and the costs for treating it are accelerating, fueled in part by the multiple co-morbidities that these patients have. Other research finds that older Medicare patients with neuromuscular-skeletal diagnoses who obtain chiropractic care have substantially lower Medicare Part B costs than those who do not. In addition, between 2003 - 2008 annual Medicare cost growth was lower for patients who used chiropractic care than those who did not. However, these findings were limited to evaluation of Medicare Part B costs and examined a very broad group of patients. This application will explore potential cost savings to Medicare associated with use of chiropractic care in patients with multiple comorbidities. Specifically, the proposed study will use data from 2006-2011 to conduct serial cross-sectional analyses that will examine the association between use of chiropractic care and healthcare costs among older Medicare patients with a diagnosis of low back pain, a musculoskeletal condition associated with low back pain, and a psychological comorbidity that might be improved should musculoskeletal pain be relieved. The conceptual model that drives the application suggests that these comorbidities might directly or indirectly benefit from chiropractic care. A serial cross sectional analysis will allow for the identificatio of patients with low back pain and multiple comorbidities. The research will compare such patients who did and who did not use chiropractic care during the year. Primary outcomes will be the average annual Total Medicare costs as well as average annual costs for each of the three Medicare components examined (Part A, Part B, and Part D). The study will inform policymakers as they consider the effective and efficient use of chiropractic care in older, sicker patients. Should evidence exist of a cost offset associated with chiropractic care, it will be used to develop an R01 grant proposal to conduct a randomized pragmatic trial designed to prospectively evaluate the effect of chiropractic care on health services utilization, costs of car, and patient outcomes among older, multiply comorbid patients.